1. Field of the Invention
The present invention relates to a photographic camera with a perforation detection device for detecting perforations of a roll film travelling across the back of the camera, and, in particular, to a photographic camera with a perforation detection device for photoelectrically detecting perforations of a roll film in which the film is prevented from being brought into contact with an photoelectric element of the perforation detection device during movement of the film as they pass the back the camera.
2. Description of Related Art
Much attention has been given to various approaches relating to structures which protect elements of a photoelectric means or device for photoelectrically detecting perforations of a film across over an exposure window of a camera. One of typical photoelectric devices comprises two separate elements, a light emitting and receiving photoelectric element and a light reflective element, or otherwise a light emitting element and a light receiving photoelectric element, disposed to face each other and allow a margin of a film in which perforations are formed to travel therebetween. When any one of the perforations is between the two elements, light emitted from the light emitting element is allowed to travel directly, or otherwise after reflection by the light reflective element, to the light receiving photoelectric element through the specific perforation. When the light receiving photoelectric element receives light passed through the specific perforation, it outputs an electric signal, detecting the specific perforation to control advancement of the film and, if necessary, other elements of the camera.
Because the two elements are disposed in close proximity to a film traveling therebetween to face each other, the film is apt to be brought into contact with either one or both of the elements. If the elements are repeatedly rubbed by the film, they suffer deterioration in photoelectric characteristics. For instance, the light reflective element is of the type having a thin sheet element coated with a thin reflective layer, the thin reflective layer can be damaged when repeatedly rubbed, leading to failures of perforation detection.
In order for the photoelectric perforation detection device of this kind to protect the elements from being rubbed by film, it is typical to place these elements in recesses or grooves having a depth sufficient to prevent film from coming into contact with the element. However, such a recess or groove forms a difference in level in the path in which a film travels which possibly catches the leader of the film, thus scratching the film and/or impeding advancement of the film. In particular, when the camera with such a structure for receiving an element of the photoelectric perforation detection device is loaded with film of the type having an open notch along a lateral edge such as described in Japanese Laid-Open Patent No. 3-168731, the difference provided by the recess almost always serves as an obstacle to movement of the film and often the notch is brought into engagement with the recess.